1. Field of the Invention
This invention relates to a layered unit provided with piezoelectric ceramics for use in actuators, diaphragms, buzzers, etc., and more particularly to a layered unit provided with piezoelectric ceramics constructed in such a manner that a piezoelectric ceramics member, and a support member which is made of ceramics such as alumina, zirconia, and forsterite, or a metallic material, or a plastic material are adhered one over the other by an adhesive agent, a method of producing the layered unit, and an ink jet printing head using such layered unit.
2. Description of the Related Art
Heretofore, there has been used a layered unit provided with piezoelectric ceramics in actuators, diaphragms, buzzers, etc. The layered unit has a structure that a plate made of piezoelectric ceramics and a support plate adapted for fixedly supporting the piezoelectric ceramics plate are adhered one over the other via an adhesive layer made of a thermosetting adhesive agent. Also, a technology has been developed recently in which such layered unit is used as part for actuators in printing heads of ink jet image forming apparatus. The actuator is operated in such a manner that pressurized ink is emitted due to deformation of the piezoelectric ceramics plate (namely, layered unit).
Such layered unit is fabricated as follows. Paste-like thermosetting adhesive agent is applied onto a surface of a support plate or a surface of a piezoelectric ceramics plate which are adhered to each other, according to squeegee method, screen printing method, offset printing method, dispenser or the like. The piezoelectric ceramics plate and the support plate are adhered one over the other in a state that an adhesive layer made of the adhesive agent applied therebetween is subjected to thermosetting while being heated and pressurized.
When adhering the piezoelectric ceramics plate and the support plate, the surface of each of these plates which are adhered to each other is lapped to make the surface smooth. After making the surfaces smooth and flat, the thermosetting adhesive agent is applied onto the surface of the support plate or the surface of the piezoelectric ceramics plate so that the paste-like adhesive agent is securely spread over the entirety of the surfaces (adhered surfaces) by pressurization.
Generally, however, it is highly likely that the paste-like thermosetting adhesive agent is hard to spread over the surface of a piezoelectric ceramics plate even if being pressurized. Also, as the adhesive agent is being spread over the entirety of the adhered surfaces of the plates, air is likely to be intruded in the adhesive agent. It is highly likely that cell is formed in the adhesive layer of the layered unit after thermosetting, with the result that an area (non-adhesive area) where the adhesive agent has not bee applied may be formed on the joint surfaces of these plates due to the existence of such cells. Consequently, adhesive strength between the piezoelectric ceramics plate and the support plate may be lessened.
In use thereof, the piezoelectric ceramics plate of the layered unit is deformed each time a voltage is applied. Accordingly, the layered unit is required to have such an adhesive strength at the adhered surface thereof as to be durable against repeated deformations of the piezoelectric ceramics plate. In the case where a desired adhesive strength is not obtained due to intrusion of air in the adhesive agent (namely, formation of cells in the adhesive layer) or formation of a non-adhesive area, it is highly likely that reliability and durability of applied products such as actuators and diaphragms may be deteriorated.
When assembling a printing head of an ink jet image forming apparatus using the layered unit, a series of cutaways which function as ink flow channels are formed in the layered unit by machining with a diamond blade. In the case where the adhesive strength of the layered unit is insufficient, the layered unit may be broken at the poorly adhered part or the layer(s) constituting the layered unit may be peeled off during formation of these cutaways, which leads to increase of occurrence of assembly failure in a process of producing printing heads.
In view of the above, an object of this invention is to provide a layered unit having an increased adhesive strength due to lowering of cell content in an adhesive layer combined with improved spreadability of adhesive agent by an improvement on a surface of a piezoelectric ceramics member of the layered unit, a method for producing the layered unit, and an ink jet printing head incorporated with such layered unit having improved ink emission precision and durability as well as suppressing occurrence of assembly failure at the time of producing the printing head.
According to an aspect of this invention, a layered unit comprises a first member made of piezoelectric ceramics; a second member which is placed over the first member; and an adhesive layer which is formed between the first member and the second member to adhere the first member and the second member. A joint surface of the first member to be jointed to the second member is formed with a multitude of recesses. A sum of opening areas of the recesses occupying 50% or more relative to a total surface area of the joint surface of the first member. Alternatively, a crystalline part composing the joint surface of the first member is formed with a multitude of microprotrusions.
According to another aspect of this invention, a method of producing a layered unit having an improved adhesive strength comprises using piezoelectric ceramics containing lead zirconate titanate in which a total content of alumina (Al2O3) and silicon oxide (SiO2) relative to the piezoelectric ceramics is 0.08 mass % or less, as a material for a first member. The method has a step of forming a multitude of recesses in a joint surface of a first member to be jointed to a second member by lapping the joint surface by grains of silicon carbide having a grain diameter in the range from 5 to 10 xcexcm as free abrasive grains, or by grinding with a diamond wheel leaving diamond grains of a grain diameter in the range from 5 to 10 xcexcm. As an altered arrangement, the method has a stop of forming a multitude of microprotrusions on a crystalline part of the joint surface of the first member by plasma treatment. Subsequently, an adhesive agent is applied onto at least one of the joint surface of the first member and a surface of the second member to adhere the first member and the second member to form a joint unit. Then, the adhesive agent is cured while pressurizing the joint unit.
According to still another aspect of this invention, an ink jet printing head comprises a base plate; an array of ink flow channels each defined by a pair of partition walls composed of a piezoelectric member, the ink flow channels being arrayed on the base plate in a widthwise direction of the ink jet printing head at a certain interval; and pairs of electrodes each provided at opposing sides of each partition wall to apply a voltage to deform the partition walls.
It may be preferable to form a multitude of recesses in the joint surface of the partition wall to be jointed to the base plate in such a manner that a surface area ratio of the recesses relative to a total surface area of the joint surface is set at 50% or more and to adhere the partition wall and the base plate by the adhesive agent. Alternatively, it may be preferable to form a multitude of microprotrusions on the joint surface of the partition wall to be jointed to the base plate and adhere the partition wall and the base plate by the adhesive agent.
These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawing.